This invention relates to injection devices.
After any injection, the syringe with its needle is thrown away into a guarded enclosure, for obvious safety reasons. But removing it from a re-usable device that first fires the syringe forwards to make the needle penetrate, then pushes the syringe piston forwards to eject the dose, and which finally withdraws the syringe and needle, can itself be hazardous and time-consuming.
One answer is to discard everything, but such injection devices are complex and expensive. That is not therefore a realistic option.
However, by making the device in two parts, one being a re-usable firing mechanism with a plunger that can be released to spring forwards, and the other being a housing and guide for the syringe to which the firing mechanism can be temporarily attached, it becomes possible to contemplate throwing away this other part (still containing a syringe).
It is the aim of this invention to provide such a device.
According to one aspect of the present invention there is provided an injection device comprising a barrel, a syringe carrier within the barrel axially movable between a rearward position, in which the needle of a syringe carried thereby is retracted within the forward end of the barrel, and a forward position, in which the needle projects from the forward end of the barrel, spring means urging the carrier towards the rearward position, and a firing mechanism with a firing member which, when released, acts on the piston in the syringe to urge the syringe forwards and then to eject a dose, characterised in that the firing mechanism is separable from the barrel and in that there is a connector with limited freedom of axial movement at the rear end of the barrel for attachment of the firing mechanism, the connector initially being held at a rearward position by the spring means acting through the syringe carrier, but moving to a forward position, taking the syringe carrier with it, as the barrel is held against the skin by the firing device being pressed forwards, the syringe carrier then being in an intermediate position from which it can be propelled to its forward position on actuation of the firing mechanism, and the connector reverting under the influence of the spring means to its rearward position after removal of the injection device from the skin.
The spring means will act through the carrier, the syringe, the firing member and its device to cause the reversion of the connector to its rearward position.
Conveniently, the attachment is by mating screw threads, the connector being restrained against rotation with respect to the barrel.
The connector may be a stepped tube, the smaller diameter portion at the rear end providing a socket to receive the firing device, the internal forward facing shoulder formed by the step providing an abutment for the rear end of the syringe carrier, and the external, rearward facing shoulder formed by the step providing an abutment for engagement with a locking ring, fitted to the rear end of the barrel, when the connector is at its rearward position.
The syringe carrier may have a lost-motion connection with the connector, and this will define the limit of the carrier""s forward movement. The larger diameter portion of the stepped tube connector may have axially parallel slots in which projections from the rear end of the syringe carrier engage to form the lost-motion connection.
The barrel will generally be internally equipped with guide means for keeping the syringe carrier co-axial therewith.
The spring means is conveniently a coil spring surrounding the syringe carrier to engage a flange at the rear end thereof and reacting against an abutment within the barrel. This abutment may be provided by the rear end of the guide means.
Preferably, the forward end of the barrel is equipped with means for effectively altering its length and thus the amount by which the needle of the syringe will project.
According to another aspect of the present invention there is provided injection equipment comprising a plurality of disposable syringe devices which have retracted needles in the pre-use and post-use conditions, a firing mechanism which can be screw-fitted to the rear end of each device, and a housing for said devices, the leading ends of each syringe device being screw-threadedly engageable with locators in the housing, these screw threads being of opposite hand to that of the firing mechanism whereby, for use of a syringe device located in the housing, the firing mechanism is screwed to its rear end and the screw action continued until the syringe device releases from its locator, and post-use the syringe device is screwed back on its locator using the firing mechanism and the screw action continued until the firing mechanism releases from the syringe device.
Preferably each pre-use syringe device has a rear end cap removable to allow screw attachment of the firing mechanism.